This invention concerns an improved process for preparing glycolic acid by the hydrogen fluoride (HF) catalyzed reaction of formaldehyde and carbon monoxide. In particular, the invention provides a method for reducing by-product formation while increasing the reaction rate by carrying out the reaction in a medium comprising a minor amount of acetic acid.
U.S. Pat. No. 3,911,003, which issued Oct. 7, 1975 to Shigeto Suzuki, describes the HF-catalyzed carbonylation of formaldehyde to glycolic acid. The reaction produces a mixture of glycolic acid and diglycolic acid. However, the yield of glycolic acid can be maximized by carrying out the reaction using aqueous formaldehyde. Where glycolic acid is the desired product, it is especially advantageous to maximize the reaction rate and minimize the formation of by-product.
U.S. Pat. No. 4,016,208, which issued Apr. 5, 1977, to Shigeto Suzuki, describes the carbonylation of formaldehyde using a catalyst comprising HF. Again the reaction produces a mixture of glycolic acid and diglycolic acid. The yield of glycolic acid can be maximized by carrying out the reaction in the presence of added water.
U.S. Pat. No. 3,948,986, which issued on Apr. 6, 1976, to Shigeto Suzuki describes the preparation of an alpha-acyloxy acid by the HF-catalyzed reaction of a C.sub.2 -C.sub.16 saturated aldehyde, carbon monoxide, and a C.sub.1 -C.sub.6 saturated carboxylic acid. In Example 5 of this patent, the HF-catalyzed reaction of acetaldehyde, carbon monoxide and acetic acid is illustrated. Acetyl lactic acid was the principal reaction product.
U.S. Pat. No. 3,948,977, which issued on Apr. 6, 1976 to Shigeto Suzuki, describes the preparation of acyloxyacetic acid by the HF-catalyzed reaction of formaldehyde, carbon monoxide and a carboxylic acid. In Example 9, the HF-catalyzed reaction of formaldehyde, carbon monoxide and acetic acid is illustrated. The product contained 86% acetoxyacetic acid.